Post-objective scanning beam systems

ABSTRACT

Scanning beam systems, apparatus and techniques in optical post-objective designs with two beam scanners for display and other applications.

This application claims the benefit of U.S. provisional application No.60/910,644 entitled POST-OBJECTIVE SCANNING BEAM SYSTEMS” and filed onApr. 6, 2007, the entire disclosure of which is incorporated byreference as part of the specification of this application.

BACKGROUND

This application relates to scanning-beam systems for producing opticalpatterns in various applications.

Scanning beam systems can be used to project one or more scanned beamson a surface to produce optical patterns. Many laser printing systemsuse a scanning laser beam to print on a printing surface of a printingmedium (e.g., paper). Some display systems use 2-dimensionally scannedlight to produce images on a screen.

As an example, many display systems such as laser display systems use apolygon scanner with multiple reflective facets to provide horizontalscanning and a vertical scanning mirror such as a galvo-driven mirror toprovide vertical scanning. In operation, one facet of the polygonscanner scans one horizontal line as the polygon scanner spins to changethe orientation and position of the facet and the next facet scans thenext horizontal line. The horizontal scanning and the vertical scanningare synchronized to each other to project images on the screen.

Some scanning-beam systems such as scanning-beam display systems use apre-objective optical design where a scan lens is placed in the opticalpath downstream from the polygon scanner and the vertical scanner tofocus a scanning beam onto a target surface, e.g., a screen. Because thescan lens is positioned downstream from the polygon scanner and thevertical scanner, the beam entering the scan lens is scanned along thevertical and horizontal directions. Therefore, the scan lens is designedto focus the 2-dimensionally scanned beam onto the target surface.

SUMMARY

The specification of this application describes, among others, scanningbeam systems, apparatus and techniques in optical post-objective designswith two beam scanners for display and other applications.

In one implementation, a scanning beam system includes a light sourceoperable to produce a beam of light; a first beam scanner to scan thebeam of light along a first direction; a second beam scanner to scan thebeam of light received from the first beam scanner along a seconddirection different from the first direction; and a scan lens placed inan optical path of the beam of light between the first and the secondbeam scanners to direct the beam of light from the first beam scanneralong a line on the second beam scanner and to focus the beam of lightonto a surface away from the second beam scanner. The system may includea beam focusing element placed in an optical path of the beam of lightto adjust a focus of the beam of light; and an actuator coupled to thebeam focusing element to adjust a position of the beam focusing element,in response to a control signal, to adjust the focus in synchronizationwith scanning of the second beam scanner.

In another implementation, a scanning beam system includes an opticalmodule operable to produce a scanning beam of excitation light havingoptical pulses that can be used to carry image information; and afluorescent screen which absorbs the excitation light and emits visiblefluorescent light to produce images carried by the scanning beam. Theoptical module includes a light source to produce the beam of excitationlight; a horizontal polygon scanner to scan the beam of excitation lightalong a first direction; a vertical scanner to scan the beam ofexcitation light from the polygon along a second direction differentfrom the first direction; and a 1-dimensional scan lens placed betweenthe polygon scanner and the vertical scanner to direct the beam ofexcitation light from the polygon scanner along a line on the verticalscanner and to focus the beam of excitation light onto the screen.

In another implementation, a scanning beam system includes a lightsource to produce a beam of light having optical pulses that carry imageinformation; a horizontal polygon scanner to scan the beam along a firstdirection at a first scanning rate; a vertical scanner to scan the beamfrom the polygon along a second direction different from the firstdirection at a second scanning rate less than the first scanning rate; a1-dimension scan lens placed between the polygon scanner and thevertical scanner to direct the beam from the polygon scanner along aline on the vertical scanner and to focus the beam onto a referencesurface; a beam focusing element placed between the light source and thehorizontal polygon scanner to adjust a focus of the beam on thereference surface; and an actuator coupled to the beam focusing elementto adjust a position of the beam focusing element, in response to acontrol signal, to adjust the focus in synchronization with a scanningposition of the vertical scanner.

In yet another implementation, a method for scanning a beam along twodirections on a target surface includes scanning the beam with a firstscanner to scan the beam along a first direction at a first scanningrate; directing the beam out of the first scanner into a second scannerto scan the beam along a second direction different from the firstdirection at a second scanning rate less than the first scanning rate;using a 1-dimension scan lens placed between the first and the secondscanners to focus the beam onto the target surface; and controlling afocus of the beam in synchronization with a scanning position of thesecond scanner to control focusing of the beam on the target surface.

These and other implementations are described in detail in the drawings,the detailed description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example implementation of a post-objective scanningsystem.

FIGS. 2A and 2B show two examples of a laser source for modulatinginformation onto a scanning beam in the system of FIG. 1.

FIG. 3A illustrates an example of a fluorescent screen having colorphosphor stripes that can be used in a post-objective scanning beamdisplay system.

FIG. 3B shows an exemplary design of the screen in FIG. 3A.

FIG. 3C shows the operation of the screen in a view along the directionperpendicular to the surface of the screen in FIG. 3A.

FIG. 4 shows another exemplary design of the screen in FIG. 3A.

FIG. 5 shows an example of a post-objective scanning beam display systembased on the system design in FIG. 1.

FIGS. 6A, 6B and 6C illustrate a specific example of the post-objectivedesign of the beam scanning module in FIG. 5.

FIGS. 7, 8 and 9 show various image effects on the screen of apost-objective scanning system.

FIG. 10 shows an example of a post-objective scanning display based on afolded optical rear projection design.

FIGS. 11-13 show examples of the vertical scanner for post-objectivescanning systems.

DETAILED DESCRIPTION

Examples of post-objective scanning-beam systems described in thisapplication use a vertical scanner with an optical reflector and aspinning horizontal polygon scanner with reflective facets to providethe 2-dimensional scanning of one or more scanning beams onto a targetscreen. A beam can be first directed to a first scanner of the verticalscanner and the polygon scanner to scan along a first direction and thendirected through a scan lens located between the vertical scanner andthe polygon scanner. After exiting the scan lens, the beam is scannedalong the first direction and is directed to the second scanner of thevertical scanner and the polygon scanner to scan along a second,different direction (e.g., orthogonal to the first direction). Theoutput of the second scanner is a scanning beam that is scanned alongboth the first and the second directions.

FIG. 1 shows an example implementation of a post-objective scanningsystem. A laser source 110 is provided to produce at least one laserbeam 112. Depending on the specific applications, this single beam canbe a beam of a particular wavelength, e.g., a visible color, UV light orother wavelengths. In some applications, multiple beams 112 may begenerated from the laser source 110 and are scanned. The different beams112 may be of different wavelengths, e.g., red, green and blue colors inthe visible range, or of the same or similar wavelengths, e.g., UVlight. In this example, the first scanner of the two scanners is apolygon scanner 140. The beam 112 is scanned along the first direction(e.g., the horizontal direction) by the polygon scanner 140 as a 1-Dscanning beam 114. The second scanner downstream from the polygonscanner 140 is a vertical scanner 150, e.g., a galvo mirror constructedby engaging a mirror to a galvanometer and operates to scan thehorizontally scanning beam 114 along the vertical direction as a 2-Dscanning beam 116 to a target surface 101, e.g., a screen. A scan lens120 is placed between the two scanners 140 and 150.

In this post-objective design, the scan lens 120 can be structured tohave high optical performance in focusing the 1-D scanning beam 114along the scanning direction of the first scanner 140 only. Hence, sucha scan lens does need to exhibit high optical performance along thesecond scanning direction (i.e., the vertical direction in this example)because the beam 114 is not scanned along the second scanning directionat the position of the scan lens 120. Therefore, the scan lens 120 canbe a 1-D scan lens, e.g., a 1-D f theta lens. High-cost and complex 2-Dlenses can be avoided in implementing the system of FIG. 1. Due to thedesign of the scan lens 120, the focusing of the beam 116 on the targetsurface 101 does not change with the horizontal scanning.

In another aspect, the vertical scanner 150 in FIG. 1 scans at a muchsmaller rate as the second scanner than the scan rate of the firsthorizontal scanner 140 and thus a focusing variation caused by thevertical scanning on the target surface 101 varies with time at theslower vertical scanning rate. This allows a focusing adjustmentmechanism to be implemented in the system of FIG. 1 with the lower limitof a response speed at the slower vertical scanning rate rather than thehigh horizontal scanning rate. In practical devices, this particulararrangement of two scanners 140 and 150 allows easy implementation ofthe dynamic focusing adjustment to maintain the proper focusing of the2-D scanning beam on the target surface as the vertical scanner 150scans along the vertical direction.

The target surface 101 in FIG. 1 is a surface of a target device 102.The device 102 can be in various forms depending on the applications ofthe system in FIG. 1. For example, in display applications, the targetdevice 102 can be a screen on which images carried by the scanning beam116 are displayed in a way visible to a viewer. The beam 112 incident tothe first scanner 140 is optically modulated to carry the images to bedisplayed on the screen 102.

FIGS. 2A and 2B show two optical modulation designs that can be used tomodulate the beam 112 to carry images or other information. In FIG. 2A,a laser 210 such as a diode laser is directly modulated to produce amodulated beam 112 that carries the image signals, e.g., color imagedata in red, green and blue. The laser source 110 in this implementationincludes a signal modulation controller 220 which modulates the laser210 directly. For example, the signal modulation controller 220 cancontrol the driving current of a laser diode as the laser 210. In FIG.2B, a laser 230 is used to generate a CW unmodulated laser beam 232 andan optical modulator 240 is used to modulate the CW laser beam 232 withthe image signals in red, green and blue and to produce the modulatedbeam 112. A signal modulation controller 250 is used to control theoptical modulator 240. For example, an acousto-optic modulator or anelectro-optic modulator may be used as the optical modulator 240.

The screen 102 can be passive screens and active screens. A passivescreen does not emit light but makes light of the one or more scanningbeams visible to a viewer by one or a combination of mechanisms, such asoptical reflection, optical diffusion, optical scattering and opticaldiffraction. For example, a passive screen can reflect or scatterreceived scanning beam(s) to show images.

An active screen emits light by absorbing the one or more scanning beamsand the emitted light forms part of or all of the light that forms thedisplayed images. Such an active screen may include one or morefluorescent materials to emit light under optical excitation of the oneor more scanning beams received by the screen to produce images. Theterm “a fluorescent material” is used here to cover both fluorescentmaterials and phosphorescent materials. Screens with phosphor materialsunder excitation of one or more scanning excitation laser beams aredescribed here as specific implementation examples of optically excitedfluorescent or phosphorescent materials in various systems.

Various screen designs with fluorescent materials can be used. Screenswith phosphor materials under excitation of one or more scanningexcitation laser beams are described in details and are used as specificimplementation examples of optically excited fluorescent materials invarious system and device examples in this application. In oneimplementation, for example, three different color phosphors that areoptically excitable by the laser beam to respectively produce light inred, green, and blue colors suitable for forming color images can beformed on the screen as repetitive red, green and blue phosphor stripesin parallel. Various examples described in this application use screenswith parallel color phosphor stripes for emitting light in red, green,and blue to illustrate various features of the laser-based displays.Phosphor materials are one type of fluorescent materials. Variousdescribed systems, devices and features in the examples that usephosphors as the fluorescent materials are applicable to displays withscreens made of other optically excitable, light-emitting, non-phosphorfluorescent materials.

For example, quantum dot materials emit light under proper opticalexcitation and thus can be used as the fluorescent materials for systemsand devices in this application. More specifically, semiconductorcompounds such as, among others, CdSe and PbS, can be fabricated in formof particles with a diameter on the order of the exciton Bohr radius ofthe compounds as quantum dot materials to emit light. To produce lightof different colors, different quantum dot materials with differentenergy band gap structures may be used to emit different colors underthe same excitation light. Some quantum dots are between 2 and 10nanometers in size and include approximately tens of atoms such between10 to 50 atoms. Quantum dots may be dispersed and mixed in variousmaterials to form liquid solutions, powders, jelly-like matrix materialsand solids (e.g., solid solutions). Quantum dot films or film stripesmay be formed on a substrate as a screen for a system or device in thisapplication. In one implementation, for example, three different quantumdot materials can be designed and engineered to be optically excited bythe scanning laser beam as the optical pump to produce light in red,green, and blue colors suitable for forming color images. Such quantumdots may be formed on the screen as pixel dots arranged in parallellines (e.g., repetitive sequential red pixel dot line, green pixel dotline and blue pixel dot line).

Some implementations of post-objective scanning beam display systemsdescribed here use at least one scanning laser beam to excite colorlight-emitting materials deposited on a screen to produce color images.The scanning laser beam is modulated to carry images in red, green andblue colors or in other visible colors and is controlled in such a waythat the laser beam excites the color light-emitting materials in red,green and blue colors with images in red, green and blue colors,respectively. Hence, the scanning laser beam carries the images but doesnot directly produce the visible light seen by a viewer. Instead, thecolor light-emitting fluorescent materials on the screen absorb theenergy of the scanning laser beam and emit visible light in red, greenand blue or other colors to generate actual color images seen by theviewer.

Laser excitation of the fluorescent materials using one or more laserbeams with energy sufficient to cause the fluorescent materials to emitlight or to luminance is one of various forms of optical excitation. Inother implementations, the optical excitation may be generated by anon-laser light source that is sufficiently energetic to excite thefluorescent materials used in the screen. Examples of non-laserexcitation light sources include various light-emitting diodes (LEDs),light lamps and other light sources that produce light at a wavelengthor a spectral band to excite a fluorescent material that converts thelight of a higher energy into light of lower energy in the visiblerange. The excitation optical beam that excites a fluorescent materialon the screen can be at a frequency or in a spectral range that ishigher in frequency than the frequency of the emitted visible light bythe fluorescent material. Accordingly, the excitation optical beam maybe in the violet spectral range and the ultra violet (UV) spectralrange, e.g., wavelengths under 420 nm. In the examples described below,UV light or a UV laser beam is used as an example of the excitationlight for a phosphor material or other fluorescent material and may belight at other wavelength.

FIG. 3A illustrates an example of a fluorescent screen 301 having colorphosphor stripes. Alternatively, color phosphor dots may also be used todefine the image pixels on the screen. The screen 301 has parallel colorphosphor stripes in the vertical direction where red phosphor absorbsthe laser light to emit light in red, green phosphor absorbs the laserlight to emit light in green and blue phosphor absorbs the laser lightto emit light in blue. Adjacent three color phosphor stripes are inthree different colors. One particular spatial color sequence of thestripes is shown in FIG. 3A as red, green and blue. Other colorsequences may also be used. The laser beam 116 is at the wavelengthwithin the optical absorption bandwidth of the color phosphors and isusually at a wavelength shorter than the visible blue and the green andred colors for the color images. As an example, the color phosphors maybe phosphors that absorb UV light in the spectral range from about 380nm to about 420 nm to produce desired red, green and blue light.

FIG. 3B shows an exemplary design of the screen 301 in FIG. 3A. Thescreen 301 in this particular example includes a rear substrate 311which is transparent to the scanning laser beam 116 to receive thescanning laser beam 116. A second front substrate 312 is fixed relativeto the rear substrate 311 and faces the viewer so that the fluorescentlight transmits through the substrate 312 towards the viewer. A colorphosphor stripe layer 310 is placed between the substrates 311 and 312and includes phosphor stripes. The color phosphor stripes for emittingred, green and blue colors are represented by “R”, “G” and “B,”respectively. The front substrate 312 is transparent to the red, greenand blue colors emitted by the phosphor stripes. The substrates 311 and312 may be made of various materials, including glass or plastic panels.Each color pixel includes portions of three adjacent color phosphorstripes in the horizontal direction and its vertical dimension isdefined by the beam spread of the laser beam 116 in the verticaldirection. As such, each color pixel includes three subpixels of threedifferent colors (e.g., the red, green and blue). In the specific momentduring the scan in FIG. 2A, the scanning laser beam 116 is directed atthe green phosphor stripe within a pixel to produce green light for thatpixel.

FIG. 3C further shows the operation of the screen 301 in a view alongthe direction perpendicular to the surface of the screen 301. Since eachcolor stripe is longitudinal in shape, the cross section of the beam 116may be shaped to be elongated along the direction of the stripe tomaximize the fill factor of the beam within each color stripe for apixel. This may be achieved by using a beam shaping optical element. Alaser source that is used to produce a scanning laser beam that excitesa phosphor material on the screen may be a single mode laser or amultimode laser. The laser may also be a single mode along the directionperpendicular to the elongated direction phosphor stripes to have asmall beam spread that is confined by the width of each phosphor stripe.Along the elongated direction of the phosphor stripes, this laser beammay have multiple modes to spread over a larger area than the beamspread in the direction across the phosphor stripe. This use of a laserbeam with a single mode in one direction to have a small beam footprinton the screen and multiple modes in the perpendicular direction to havea larger footprint on the screen allows the beam to be shaped to fit theelongated color subpixel on the screen and to provide sufficient laserpower in the beam via the multimodes to ensure sufficient brightness ofthe screen.

Alternatively, FIG. 4 illustrates an example of a fluorescent screendesign that has a contiguous and uniform layer 420 of mixed phosphors.This mixed phosphor layer 420 is designed and constructed to emit whitelight under optical excitation of the excitation light 116. The mixedphosphors in the mixed phosphor layer 420 can be designed in variousways and a number of compositions for the mixed phosphors that emitwhite light are known and documented. Notably, a layer 410 of colorfilters, such as stripes of red-transmitting, green-transmitting andblue-transmitting filters, is placed on the viewer side of the mixedphosphor layer 420 to filter the white light and to produce coloredoutput light. The layers 410 and 420 can be sandwiched betweensubstrates 401 and 402. The color filters may be implemented in variousconfigurations, including in designs similar to the color filters usedin color LCD panels. In each color filter region e.g., ared-transmitting filter, the filter transmits the red light and absorbslight of other colors including green light and blue light. Each filterin the layer 410 may be a multi-layer structure that effectuates aband-pass interference filter with a desired transmission band. Variousdesigns and techniques may be used for designing and constructing suchfilters. U.S. Pat. No. 5,587,818 entitled “Three color LCD with a blackmatrix and red and/or blue filters on one substrate and with greenfilters and red and/or blue filters on the opposite substrate,” and U.S.Pat. No. 5,684,552 entitled “Color liquid crystal display having a colorfilter composed of multilayer thin films,” for example, describe red,green and blue filters that may be used in the screen design in FIG. 4.Hence, a fluorescent stripe in the fluorescent screen in variousexamples described in this application is a fluorescent stripe thatemits a designated color under optical excitation and can be either afluorescent stripe formed of a particular fluorescent material thatemits the designated color in FIG. 3A or a combination of a stripe colorfilter and a white fluorescent layer in FIG. 4.

FIG. 5 shows an example implementation of a post-objective scanning beamdisplay system based on the system design in FIG. 1. A laser array 510with multiple lasers is used to generate multiple laser beams 512 tosimultaneously scan a screen 501 for enhanced display brightness. Thescreen 501 can be a passive screen or an active screen. The laser array510 can be implemented in various configurations, such as discrete laserdiodes on separate chips arranged in an array and a monolithic laserarray chip having integrated laser diodes arranged in an array. A signalmodulation controller 520 is provided to control and modulate the lasersin the laser array 510 so that the laser beams 512 are modulated tocarry the image to be displayed on the screen 501. The signal modulationcontroller 520 can include a digital image processor which generates thedigital image signals for the three different color channels and laserdriver circuits that produce laser control signals carrying the digitalimage signals. The laser control signals are then applied to modulatethe lasers in the laser array 510, e.g., electric currents that drivethe laser diodes. The laser beams 512 can be of different wavelengths(e.g., red, green and blue colors for a display with a passive screen501) or of the same wavelength (e.g., either to increase the intensityof light to produce a monochromatic pattern on a passive surface 501 oran excitation light beam that excites phosphors on an active phosphorscreen 501 in FIG. 3A).

The beam scanning is based on a two-scanner system in FIG. 1. Each ofthe different reflective facets of the polygon scanner 140simultaneously scans N horizontal lines where N is the number of lasers.A relay optics module 530 reduces the spacing of laser beams 512 to forma compact set of laser beams 532 that spread within the facet dimensionof the polygon scanner 140 for the horizontal scanning. Downstream fromthe polygon scanner 140, there is a 1-D horizontal scan lens 120followed by a vertical scanner 150 (e.g., a galvo mirror) that receiveseach horizontally scanned beam 532 from the polygon scanner 140 throughthe 1-D scan lens 120 and provides the vertical scan on eachhorizontally scanned beam 532 at the end of each horizontal scan priorto the next horizontal scan by the next facet of the polygon scanner140.

Under this optical design of the horizontal and vertical scanning, the1-D scan lens 120 is placed downstream from the polygon scanner 140 andupstream from the vertical scanner 150 to focus each horizontal scannedbeam on the screen 501 and minimizes the horizontal bow distortion todisplayed images on the screen 501 within an acceptable range, thusproducing a visually “straight” horizontal scan line on the screen 501.Such a 1-D scan lens 120 capable of producing a straight horizontal scanline is relatively simpler and less expensive than a 2-D scan lens ofsimilar performance. Downstream from the scan lens 120, the verticalscanner 150 is a flat reflector and simply reflects the beam to thescreen 501 and scans vertically to place each horizontally scanned beamat different vertical positions on the screen 501 for scanning differenthorizontal lines. The dimension of the reflector on the vertical scanner150 along the horizontal direction is sufficiently large to cover thespatial extent of each scanning beam coming from the polygon scanner 140and the scan lens 120. The system in FIG. 5 is a post-objective designbecause the 1-D scan lens 120 is upstream from the vertical scanner 150.In this particular example, there is no lens or other focusing elementdownstream from the vertical scanner 150.

This optical design eliminates the need for a complex and expensive 2-Dscan lens 120 in pre-objective scanning beam displays where the scanninglens is located downstream from the two scanners 140 and 150 and focusesthe a scanning excitation beam onto a screen. In such a pre-objectivedesign, a scanning beam directed into the scan lens is scanned along twoorthogonal directions. Therefore, the scan lens is designed to focus thescanning beam onto the screen along two orthogonal directions. In orderto achieve the proper focusing in both orthogonal directions, the scanlens can be complex and, often, are made of multiples lens elements. Inone implementation, for example, the scan lens can be a two-dimensionalf-theta lens that is designed to have a linear relation between thelocation of the focal spot on the screen and the input scan angle(theta) when the input beam is scanned around each of two orthogonalaxes perpendicular to the optic axis of the scan lens. In such a f-thetalens, the location of the focal spot on the screen is a proportional tothe input scan angle (theta).

The two-dimensional scan lens such as a f-theta lens in thepre-objective configuration can exhibit optical distortions along thetwo orthogonal scanning directions which cause beam positions on thescreen to trace a curved line. Hence, an intended straight horizontalscanning line on the screen becomes a curved line. The distortionscaused by the 2-dimensional scan lens can be visible on the screen andthus degrade the displayed image quality. One way to mitigate the bowdistortion problem is to design the scan lens with a complex lensconfiguration with multiple lens elements to reduce the bow distortions.The complex multiple lens elements can cause the final lens assembly todepart from desired f-theta conditions and thus can compromise theoptical scanning performance. The number of lens elements in theassembly usually increases as the tolerance for the distortionsdecreases. However, such a scan lens with complex multiple lens elementscan be expensive to fabricate.

To avoid the above distortion issues associated with a two-dimensionalscan lens in a pre-objective scanning beam system, the followingsections describe examples of a post-objective scanning beam displaysystem, which can be implemented to replace the two-dimensional scanlens with a simpler, less expensive 1-dimensional scan lens 120 shown inFIG. 5.

FIGS. 6A, 6B and 6C illustrate a specific example of the post-objectivedesign of the beam scanning module in FIG. 5. The 1-D scan lens 120 canbe a compound lens with multiple lens elements to achieve desired 1-Dfocusing of a horizontally scanned beam with no horizontal bowdistortion. The 1-D scan lens 120 can have an elongated shape along thehorizontal scanning direction of the beam and is placed within the sameplane 600 that is perpendicular to the vertical polygon rotation axis.The vertical scanner 150 pivots around a horizontal axis which lies inthe plane 600. The pivoting of the vertical scanner 150 directs beamsreflected from different polygon facets to different vertical directionsto trace out different horizontal scan lines on the screen 501. FIG. 6Bshows the cross section view of the beam scanning module 4920 along thelines BB in FIG. 6A which is a view along the lines AA in FIG. 6B. FIG.6C further shows a perspective view of the beam scanning module 4920 toshow different horizontal positions of a horizontally scanned beam byalong a straight horizontal line from a single polygon facet. The 1-Dscan lens 120 in the above example is a 4-element compound lens as shownin FIGS. 6A and 6B.

Notably, the distance from the scan lens to a location on the screen 501for a particular beam varies with the vertical scanning position of thevertical scanner 150. Therefore, when the 1-D scan lens 120 is designedto have a fixed focal distance along the straight horizontal line acrossthe center of the elongated 1-D scan lens, the focal properties of eachbeam must change with the vertical scanning position of the verticalscanner 150.

FIG. 7 illustrates examples of the changes in the beam size and shape onthe screen 501 for the post-objective design in FIGS. 6A-6C alongdifferent horizontal positions on the screen 501. In this pot diagramfor a horizontal set of beams at different horizontal positions and thesame vertical position on the screen, the end spots located on two sidesof the screen are more elongated because of the large angle of incidenceof the laser which is about 42 degrees in the setup for the measurementsshown.

FIG. 8 further shows beam widths at different representative positionson the screen 501: middle center, middle edge, top center and top corneror edge. Hence, in order to maintain the beam size to be at a constantsize, a dynamic focusing mechanism is implemented to adjust convergenceof the beam going into the 1-D scan lens 120 based on the verticalscanning position of the vertical scanner 150.

Referring back to FIG. 6B, an example of the dynamic focusing mechanismis illustrated. In the optical path of the one or more laser beams fromthe lasers to the polygon scanner 140, a stationary lens 620 and adynamic refocus lens 630 are used as the dynamic focusing mechanism.Each beam is focused by the dynamic focus lens 630 at a locationupstream from the stationary lens 620. When the focal point of the lens630 coincides with the focal point of the lens 620, the output lightfrom the lens 620 is collimated. Depending on the direction and amountof the deviation between the focal points of the lenses 620 and 630, theoutput light from the collimator lens 620 toward the polygon scanner 140can be either divergent or convergent. Hence, as the relative positionsof the two lenses 620 and 630 along their optic axis are adjusted, thefocus of the scanned light on the screen 501 can be adjusted.Alternatively, the lens 620 may be adjustable while the lens 630 isfixed in position or both lenses 620 and 630 are adjustable to changetheir positions for changing the focus of the beam sent to the screen.

A refocusing lens actuator 640 can be used to adjust the relativeposition between the lenses 620 and 630 in response to a control signal650. In this particular example, the refocusing lens actuator 5410 isused to adjust the convergence of the beam directed into the 1-D scanlens 120 along the optical path from the polygon scanner 140 insynchronization with the vertical scanning of the vertical scanner 150.The actuator 640 is controlled to adjust the position of the lens 630relative to an upstream focal point of the lens 620 to change the beamconvergence at the entry of the 1-D scan lens 120. A control module canbe provided to synchronize the actuator 640 and the vertical scanner 150by sending a refocusing control signal 650 to control the operation theof actuator 640. For example, if the collimation lens 620 with a focallength of 8 mm is used, then the adjustment can be a distance of lessthan 10 microns at the lens 630 to provide sufficient refocusing for ascreen of over 60″ in the diagonal dimension.

In addition to the beam size and the beam focus, the change of thedistance from the scan lens 120 to a location on the screen 501 for aparticular beam due to different vertical scanning positions of thevertical scanner 150 also creates a vertical bow distortion on thescreen 501. Assuming the vertical scanner 150 directs a beam to thecenter of the screen 501 when the vertical angle of the vertical scanner150 is at zero where the distance between the screen 501 and thevertical scanner 150 is the shortest. As the vertical scanner 150changes its vertical orientation in either vertical scanning direction,the horizontal dimension of each horizontal line increases with thevertical scanning angle.

FIG. 9 illustrates this bow distortion. Different from classical barreldistortions in lenses, this distortion is geometrical in nature and iscaused by the change in the vertical scanning angle of the verticalscanner 150. This distortion essentially changes the beam spot spacingof beam spots from a regular chain of optical pulses in each scanningbeam along the horizontal direction across the screen 501. Therefore,the above-described digital technique of controlling timing of laserpulses in the scanning beam during each horizontal scan can be appliedto correct this distortion.

During a horizontal scan, the time delay in timing of a pulse can causethe corresponding position of the laser pulse on the screen to spatiallyshift downstream along the horizontal scan direction. Conversely, anadvance in timing of a pulse can cause the corresponding position of thelaser pulse on the screen to spatially shift upstream along thehorizontal scan direction. A position of a laser pulse on the screen inthe horizontal direction can be controlled electronically or digitallyby controlling timing of optical pulses in the scanning beam. Therefore,the timing of the pulses in the scanning beam can be controlled todirect each optical pulse to a location that reduces or offsets thehorizontal displacement of the beam caused by the vertical scanning ofthe vertical scanner 150. This can be achieved by obtaining the amountsof the horizontal position shift at each beam location caused by thevertical scanning in each of all horizontal scan lines at differentvertical scanning positions on the screen. The timing of the laserpulses is then controlled during each horizontal scanning to offset theobtained amounts of the horizontal position shift at different beamlocations and at different vertical scanner positions. Notably, thiscontrol of the timing of laser pulses is separate from, and can besimultaneously implemented with, the control of timing of laser pulsesin aligning laser pulses to proper phosphor color stripes during ahorizontal scan based on the servo feedback described in PCT patentapplication No. PCT/US2007/004004 entitled “Servo-Assisted Scanning BeamDisplay Systems Using Fluorescent Screens” and filed Feb. 15, 2007 andpublished as PCT publication No. ______ on ______, and PCT patentapplication No. PCT/US2006/11757 entitled “Display Systems and DevicesHaving Screens With Optical Fluorescent Materials” and filed Mar. 31,2006 and published as PCT publication No. 2006/107720 on Oct. 12, 2006.Various servo mark designs on screens and servo feedback techniquesdescribed in the above two PCT applications can be applied to thepost-objective scanning beam systems described in this application. Theentire disclosures of the above two PCT applications are incorporated byreference as part of the specification of this application.

The post-objective designs described above can be used to reducedimension of a rear-projection display system using a folded opticalpath design. FIG. 10 shows one example of a rear-projection displaybased on a post-objective scanning beam design of this application. Thescreen 501 is placed above the plane 500 in which the polygon scanner140, the 1-D scan lens 120 and the center of the vertical scanner 150are located. The screen lower edge of the display area (e.g., the areawith fluorescent stripes in FIG. 3A) of the screen 501 is above theplane 600 by a chin height H. It can be desirable to reduce the chinheight H in such systems to reduce the size of the display. It can alsobe desirable to reduce the depth D of the display to about 13.5″ orless. A combination of the folded optical path and the post-objectiveconfiguration allows both H and D to be minimized.

In this example, the screen 501 can be approximately perpendicular tothe plane 600. A folding reflector 1010 is provided at the excitationside of the screen 501 to reflect light from the vertical scanner 150 tothe screen 501. The reflector 1010 can be oriented at an angle withrespect to the screen 501 and has one end 1011 to be close to or incontact with the upper side of the active display area of the screen 501to reflect light to the upper side the active display area. Thedimension and angle of the reflector 1010 are set to allow the other end1012 of the reflector 1010 to reflect light from the vertical scanner150 near the lower edge of the active area of the screen 501. Thevertical scanner 150 can be placed as close to the inner side of thescreen 501 as possible to minimize the depth D of the display.

In the above post-objective scanning designs, the 1-D scan lens isplaced downstream from the polygon horizontal scanner 140 which providesa high-speed horizontal scan (e.g., 1080 successive scans per frame fora 1080-p display) and upstream from the vertical scanner 150 whichprovides a lower speed vertical scan (e.g., one scan per frame). Underthis configuration, the refocusing control by the actuator 640 issynchronized with the lower-speed vertical scan of the vertical scanner150 and thus allows for a slower actuator to be used as the actuator 640for the refocusing. Accordingly, various issues associated with using ahigh-speed actuator for the refocusing mechanism, such as cost,feasibility, and refocusing speed and accuracy are avoided.

Referring to FIG. 6B, the vertical scanner 150 has a dimension Wsufficiently large to receive the horizontally scanned beam from the 1-Dscan lens 120. This dimension W is much larger (e.g., 134 mm) than thevertical scanner used in pre-objective scanning system and can presenttechnical issues in designing the vertical scanner 150. For example, thedistortion in the shape of the vertical scanner 150 can distort ahorizontal scan line and thus compromise the image quality.Electromagnetic galvo mirrors can be used to implement the verticalscanner 150.

FIGS. 11, 12 and 13 illustrate three examples where the coils aredesigned to provide a torque along the full length of the mirror. FIG.11 shows a permanent magnet type rotor with a slotted stator. In FIG.12, a permanent magnet type rotor with smooth stator windings is shown.FIG. 13 shows a stepper motor type galvo motor-mirror where the mirrorcan be hollowed out to reduce the inertia.

Notably, the various servo control techniques described in connectionwith the pre-objective display systems can be applied to thepost-objective scanning beam displays.

The post-objective scanning beam systems based on the designs describedin this application can be applied to display systems and other opticalsystems that use scanning beams to produce optical patterns. Forexample, laser printing systems can also use the above describedpost-objective scanning systems where the screen is replaced by aprinting medium (e.g., paper, fabric, or a master printing plate).

While this specification contains many specifics, these should not beconstrued as limitations on the scope of an invention or of what may beclaimed, but rather as descriptions of features specific to particularembodiments of the invention. Certain features that are described inthis specification in the context of separate embodiments can also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment canalso be implemented in multiple embodiments separately or in anysuitable sub-combination. Moreover, although features may be describedabove as acting in certain combinations and even initially claimed assuch, one or more features from a claimed combination can in some casesbe excised from the combination, and the claimed combination may bedirected to a sub-combination or a variation of a sub-combination.

Only a few implementations are disclosed. However, it is understood thatvariations and enhancements may be made.

1. A scanning beam system, comprising: a light source operable to produce a beam of light; a first beam scanner to scan the beam of light along a first direction; a second beam scanner to scan the beam of light received from the first beam scanner along a second direction different from the first direction; and a scan lens placed in an optical path of the beam of light between the first and the second beam scanners to direct the beam of light from the first beam scanner along a line on the second beam scanner and to focus the beam of light onto a surface away from the second beam scanner.
 2. The system as in claim 1, wherein: the first beam scanner scans at a first scanning rate higher than a second scanning rate of the second beam scanner.
 3. The system as in claim 2, wherein: the first beam scanner is a polygon scanner comprising a plurality of different reflective facets, and the second beam scanner is a 1-dimensional beam scanner.
 4. The system as in claim 3, wherein: the 1-dimensional beam scanner comprises a galvanometer and a reflector engaged to the galvanometer.
 5. The system as in claim 1, comprising: a beam focusing element placed in an optical path of the beam of light to adjust a focus of the beam of light; and an actuator coupled to the beam focusing element to adjust a position of the beam focusing element, in response to a control signal, to adjust the focus in synchronization with scanning of the second beam scanner.
 6. The system as in claim 5, wherein: the beam focusing element is located in an optical path of the beam of light upstream from the scan lens.
 7. The system as in claim 6, wherein: the beam focusing element is located in an optical path of the beam of light upstream from the first beam scanner.
 8. The system as in claim 5, wherein: the beam focusing element comprises a first lens and a second lens that are spaced from each other in an optical path of the beam of light, and the actuator is engaged to at least one of the first and second lenses to adjust a spacing between the first and second lenses.
 9. The system as in claim 1, wherein: the scan lens is a 1-dimensional lens.
 10. The system as in claim 1, wherein: the scan lens is a 1-dimensional f-theta lens.
 11. The system as in claim 1, comprising: a screen in an optical path of the beam of light output by the second beam scanner, the screen having the surface onto which the beam of light is focused by the scan lens.
 12. The system as in claim 11, wherein: the surface is made of a material that interacts with the beam of light to directly use light in the beam of light to present images carried in the beam of light to a viewer.
 13. The system as in claim 11, wherein: the surface is made of a material that absorbs light of the beam of light to emit light which presents images carried in the beam of light to a viewer.
 14. The system as in claim 13, wherein: the surface comprises phosphor materials.
 15. The system as in claim 13, wherein: the surface comprises parallel stripes of phosphor materials.
 16. The system as in claim 1, wherein: the light source comprises lasers that produce laser beams to constitute the beam of light.
 17. A scanning beam system, comprising: an optical module operable to produce a scanning beam of excitation light having optical pulses that can be used to carry image information; and a fluorescent screen which absorbs the excitation light and emits visible fluorescent light to produce images carried by the scanning beam, wherein the optical module comprises: a light source to produce the beam of excitation light; a horizontal polygon scanner to scan the beam of excitation light along a first direction; a vertical scanner to scan the beam of excitation light from the polygon along a second direction different from the first direction; and a 1-dimensional scan lens placed between the polygon scanner and the vertical scanner to direct the beam of excitation light from the polygon scanner along a line on the vertical scanner and to focus the beam of excitation light onto the screen.
 18. The system as in claim 17, further comprising: the screen comprises parallel fluorescent stripes which produce the images carried by the scanning beam.
 19. The system as in claim 17, further comprising: a beam focusing element placed between the light source and the horizontal polygon scanner to adjust a focus of light on the screen; an actuator coupled to the beam focusing element to adjust a position of the beam focusing element, in response to a control signal, to adjust the focus in synchronization with a scanning position of the vertical scanner.
 20. The system as in claim 19, wherein: the beam focusing element comprises two lenses separated from each other, and the actuator is engaged to at least one of the two lenses to adjust a spacing between the two lenses.
 21. A scanning beam system, comprising: a light source to produce a beam of light having optical pulses that carry image information; a horizontal polygon scanner to scan the beam along a first direction at a first scanning rate; a vertical scanner to scan the beam from the polygon along a second direction different from the first direction at a second scanning rate less than the first scanning rate; a 1-dimension scan lens placed between the polygon scanner and the vertical scanner to direct the beam from the polygon scanner along a line on the vertical scanner and to focus the beam onto a reference surface; a beam focusing element placed between the light source and the horizontal polygon scanner to adjust a focus of the beam on the reference surface; and an actuator coupled to the beam focusing element to adjust a position of the beam focusing element, in response to a control signal, to adjust the focus in synchronization with a scanning position of the vertical scanner.
 22. The system as in claim 21, wherein: the beam of light is at one wavelength.
 23. The system as in claim 21, wherein: the beam of light comprises light of at least two different wavelengths.
 24. The system as in claim 21, wherein: the beam focusing element comprises a first lens and a second lens that are spaced from each other in an optical path of the beam of light, and the actuator is engaged to at least one of the first and second lenses to adjust a spacing between the first and second lenses.
 25. The system as in claim 21, comprising: a screen located near the vertical scanner and oriented to be perpendicular to a direction from the horizontal polygon scanner to the scan lens and the vertical scanner, the screen having a screen surface as the reference surface; and a reflector positioned above the plane in which the horizontal polygon scanner, the scan lens and the vertical scanner are located and oriented to receive the beam reflected from and scanned by the vertical scanner and to reflect the beam to the screen.
 26. The system as in claim 25, wherein: the reflector is oriented to have a first end located close to a first end of the screen away from the vertical scanner to direct the beam from the vertical scanner to the first end of the screen, and a second end to direct the beam from the vertical scanner to a second end of the screen that is close to the vertical scanner.
 27. A method for scanning a beam along two directions on a target surface, comprising: scanning the beam with a first scanner to scan the beam along a first direction at a first scanning rate; directing the beam out of the first scanner into a second scanner to scan the beam along a second direction different from the first direction at a second scanning rate less than the first scanning rate; using a 1-dimension scan lens placed between the first and the second scanners to focus the beam onto the target surface; and controlling a focus of the beam in synchronization with a scanning position of the second scanner to control focusing of the beam on the target surface.
 28. The method as in claim 27, comprising: using two lenses spaced from each other in an optical path of the beam to adjust a relative position of the two lenses in controlling the focus of the beam. 